It is known to form a cross-sectional profile of a tubular member by a hydroforming process in which a fluid-filled tubular member is placed within a cavity of a die and then the die is closed so that the tubular member is pinched within the die. Fluid pressure is then increased inside the tubular member to expand the tubular member outwardly against the cavity of the die to provide a tubular member having a die formed cross-sectional profile.
During tube hydroforming, large size punches of various shapes are used to create desired openings in the tubular member by piercing. The large punches currently used, necessitate similarly large activating hydraulic cylinders in order to overcome the forces needed for piercing. Large bore hydraulic cylinders need high volume of oil flow to operate.
Using the hydroforming process, the piercing operation is performed within the die. One method of piercing used in hydroforming applications is “hydrapiercing”. Upon completion of hydroforming, the tubular member is in intimate contact with the wall of the die. The hydroforming fluid is at a forming pressure, approximately 10,000 psi. A punch is attached to a hydraulic actuated cylinder. As the water pressure reaches its peak, the cylinder is activated to move the punch to pierce the required hole for the tubular member, allowing the metal to be sheared and produce a slug.
In this operation, it is important not to loose water pressure when the tubular member is being hydroformed and pierced, otherwise, the tubular member will collapse. Presently, to overcome the loss in pressure during piercing, all hydraulic actuated cylinders must pierce simultaneously or in clusters of two or more at a time, with minimal time there between. Any small variation in hydraulic cylinder oil flow, forming pressure, hydraulic cylinder oil pressure, wall thickness, or hardness will interfere with the timing in hydraulic cylinder movement, thereby allowing some openings to be pierced before or after the programmed sequence. This ultimately contributes to uncontrolled leakage areas, which will contribute to non-repeatable tubular member definition and in most cases to the complete collapse of the tubular member resulting in scrap.
As a result, it is desirable to provide a punch to pierce openings in a tubular member during the hydroforming process. It is also desirable to provide a punch that can leave a clean pierce through the material of the tubular member. It is further desirable to provide a punch that is able to provide good slug retention as well as move the slug away from the opening. It is still further desirable to provide a punch that is able to prevent the loss of water pressure as multiple openings are being created by the punch. Therefore, there is a need in the art to provide a new punch for a hydroforming die that meets these desires.